Stabilized silver halide emulsions



Patented Feb. 5, 1946 STABILIZED SILVER HALIDE EMULSIONS Fritz W. H. Mueller, Binghamton, N. Y., asslgnor to General Aniline & Film Corporation, New

York, N. Y., a corporation of New York No Drawing. Application October 17, 1944,

Serial No. 559,127

Claims.

This invention relates to the improvement of photographic emulsions and more particularly to the incorporation of anti-fogging or stabilizing agents into silver halide emulsions.

A large number of substances have been described as being efiective in preventing an increase in fog and thus stabilizing-or controlling the keeping quality of photographic emulsions.

Many of these stabilizers have definite limitations in their ability to produce desirable eiiects without producing unfavorable side reactions. Thus, some stabilizers desensitize or produce fog. when added during the mixing or ripening, but

' exert favorable effects when added to the melted emulsion before coating. It is one object of this invention, therefore, to produce a stabilizing emulsion of improved photographic quality while incorporating the stabilizing agents over a wider range of application during the manufacture of photographic emulsions.

: In U. S. Patent 2,057,764 there is described a process of stabilizing photographic silver halide emulsions by incorporating sulfinic or seleninic acids or their salts into the emulsion in the form of a solution in a suitable solvent during the preparation of the emulsion or by incorporating the stabilizer into the finished emulsion by bathing the emulsion layer with a weak solution of the stabilizer. It was found that the fogging influence of supports, preparation .layers, backing layers, intermediate layers, sublayers, protective layers, or baryta layers could be prevented by incorporating these stabilizers into such layers. As compared with films which were not provided with the sulfinic acid or seleninic acid stabilizers, it is stated that the films containing the stabilizer, showed a fog density unit of approximately one-half. It has now been discovered that the stabilizing effect of the sulfinic or the seleninic acids or their salts, disclosed in U. S. Patent 2,057,764. can be considerably improved and the range of application greatly extended if small amounts of salts or esters of substituted or unsubstituted aliphatic, aromatic or heterocyclic thiosulfonic acids (sulfoxides) are present in the emulsion containing the sulfinates or 'seleninates. Compounds representing the salts of thiosulfonic acids have the following general formula wherein Z is a substituted or unsubstituted aromatic or heterocyclic ring or a substituted or unsubstituted aliphatic chain and M is a metal,

preferably an alkali metal, or ammonium, or

guanidinium or another organic cation.

Compounds representing the esters of thiosulfonic acid have the following general formula:

- It may be noted that the literature refers to these types of compounds alternatively as disulfoxide representing the following formula:

o-soso-Q wherein Y stands for the atoms necessary to complete an aromatic or heterocyclic ring. 4

It has been observed that extremely small quantities of the aromatic or heterocyclic sulfoxides will improve the stabilizing characteristic of photographic emulsions containing a sulfinate or seleninate to an extent unobtainable with a sulfinate or seleninate alone. Thus, the photo graphic eflect of sodium sulfinate or seleninate is improved by the addition of 0.00025-0.0050 mol per mol of sulfinate or seleninate of salts or esters of triosulfonic acids, such as diphenyl disulfoxide, ditolyl disulfoxide, dinaphthyl disulfproximately one-half the 'fog density obtained when using a sulfinate or seleninate alone. This reduction in fog density produces betterclearness, better keeping quality and an unusual brilliance which is especially desirable in medical and industrial radiographs.

The same reduction in fog density is obtained whether the aromatic or'heterocyclic sulfoxide compound is added with the sulfinate or seleninate during mixing or during the'ripenlng stage in the process of making the silver halide emulsion or to molten' emulsion prior to coating. In

the latter case, solvents for the stabilizer mix-.

' ture are employed which do not aflect emulsions may also be employed in preparation layers.

backing layers, intermediate layers, sublayers,

protectivelayersandbarytalayersinorderto prevent the logging influence of such layers.

Withoutin anywaywishingtobeboimdbyor limitedtoanypartlculartheoryastothemeehanism o! the additional stabilizing efl'ect produced by the aromatic or heterocyclic sulioxide.

it is believed that this additional stab eflect is either "a catalytic one or is due to a chemical interaction between the sulioxide compound and the sulilnate or selenlnate with the possible production of a reaction product which exerts the enhanced stabilizing influence on the silver halide emulsion. The iollowing examples will serve to iurther illustrate the invention. it being understood that the inventlon is not limited thereto:

Example I To 1 kilogram oi a gelatino-silver-hallde emulsion containing from 8 to 7% 01 silver halide and approximately 8% gelatin, there were added during the ripening stage:

15 cc. 01' a 20% solution oi the sodium salt of benzene sulnnlc acid in .water and 3.5 cc. of an alcoholic solution of diphenyldis'ulioxide of the concentration or one gram per liter of methanol.

The melted emulsion was then cast on a film base and cut into test film lengths. Additional similar test films were made with the same silver halide emulsion to which had been added during ripening the same quantity of the sodium salt benzene sulfinic acid as above but omitting the diphenyl-disulioxide.

The log density of each of these types of test. film was determined for the freshly prepared film and test pieces of each type were then incubated for a period of six days at 50' C. It was observed that the fog density of the films treated with benzene sulfinic acid to which had been added diphenyl-disuli'oxide was considerably improved as compared with the log density of the films which had been treated with benzene sulfinic acid alone. In terms of percentage reduction of the fog density of the film treated only with the benzene sulfinic acid, the addition of the diphenyl disulioxide in accordance with this example reduced the fog density by 66 to 68% in the case of the freshly prepared film and byjfi to 67% in the case 01' the incubated film.

Example I! To 1 kilogram of a gelatino-silver-halide emulsion containing from 6 to 7% of silver halide and approximately 8% gelatin, there were added during the ripening stage:

10 cc. of a solution of sodium salt of benzene seleninic acid and 2 cc. of a solution of sodium benzene thiosulionate (CeI-Is.SOz.SNa.1%H:O) oi the concentration of one gram per liter of water.

observed that the log density of the illms treated with benzene seleninic acid to which had been Wis amiss added sodlumbenzene thiosullonate was considerably improved as compared with the log densityoithefilmswhichhadbeentreatedwlth benzene seleninic acid alone. In terms of percentage of the fog density of the film treated only with the benzene seleninic acid the reduction oi tog density due to the sodium benzene thiosulionate was of the same order as in the case of Example I.

Example HI To a gelatino-silver-halide emulsion corresponding to grams of silver, there were added aiter precipitation of silver halide and prior to the first digestion:

taining 1 gram in 1 liter of water made slightly alkaline with NH:

The emulsion thus prepared was then washed and alter-ripened in the usual manner. For comparison, a similar emulsion was prepared "and treated in the same way but omitting the lcystine-disulfoxide addition. It was observed that the clearness and keeping quality of the emulsion prepared in accordance with this example were considerably improved over the comparison emulsion which did not contain the above mentioned cystine derivative.

Tests made ,for log density in the same manner as outlined in the preceding examples showed that the addition of the l-cystine-disultoxic'e efiected a reduction in the fog density 01 the-film containing only the sodium benzene sulfinate oi the same order as observed in cases of the diphenyl-disultoxide and the sodium benezene thiosulionate.

The improvement obtainable when the fog characteristic is expressed in density units will, of course, vary somewhat depending upon the type of gelatin and the formula used in making the gelatino-sllver-halide emulsion. The following table which expresses average i'og values based upon the tests referred to in the examples will serve to further illustrate the improvement which is achieved by using the salts or esters of aromatic or heteocyclic thiosulionic acids in combination with the sulfinates or seleninates as additions to typical gelatino-silver-halide emulsions:

Fog after Fog oi the Type of film n-eshly 6 gagi coated film Sago Film with the addition cl sodium benzene sulilnate or seleninate as a Density units Density units coating ilnai 0. 25-0. 30 0. 25-0. 35 Film with the addition of sodium benzene sulflnate or selinate and aromatic or heterocycllc sulfoxides.-.. 0. 12-0. 15 0. 15-0. 19 Film made from emulsion to which had been added sodium sulfinate or selenlnate during ripening 0. 38-0. 45 0. 45-0. 55 Film made from emulsion to which had been added during the ripening sodium sulfinate or seleninate in combination with aromatic or heterocyclic sulioxide compounds 0. 12-0. 15 0. 15-0. 19

What I claim as'my invention and desire to be secured by Letters Patent of the United States 1. A photographic material comprising a-silver halide gelatin emulsion .in contact with a member of the group consisting of a sulfinic acid, a seleninic acid and their salts, and a sulfoxide compound selected from the group consisting of aromatic and heterocyclic sultoxlde compounds of the following structural formulae:

wherein Z is a member of the group consisting of alkyl, arm and heterocyclic radicals; Y represents the atoms necessary to complete a member of the group consisting of aromatic and heterocyclic rings; and M is a member of the group consisting of metallic atoms and organic cations.

2. A photographic material comprisingva silver halide gelatin emulsion containing a member of the group consisting of a sulflnic acid, a seieninic acid and their salts, and a sulfoxide compound selected from the group consisting of aromatic wherein Z is a member of th group consisting of alkyl, aryl, and heterocyclic radicals; Y represents the atoms necessary to complete a member of-the group consisting of aromatic and heterocyclic rings; and M is a member of the group consisting of metallic atoms and organic cations. I

3. A photographic material comprising a silver halide gelatin emulsion in contact with a member of the group consisting of a sulfinic acid, a seleninic acid and their salts, and small amounts of diphenyl disulfoxide.

4. A photographic material comprising a silver halide gelatin emulsion in-contact with a member of the g oup consisting of a sulfinic acid, a

. seleninic acid and their salts. and small amounts of l-cystine-disulfoxide.

5. A photographic material comprising a silver halide gelatin emulsion in contact with a memheterocycnc Sulfoxide having-the 20 her of the group consisting of a suliinic acid, a

following structural formulae:

seleninic acid and their salts, and small amountsof sodium benzene thiosultonate.

FRITZ w. H. MUELLER. 

